1. Field of the Invention
The present invention relates to a volumetric ultrafiltration system and its method of use, a volumetric infusion system and its method of use, and more particularly, concerns a method and apparatus for controlling ultrafiltration during hemodialysis.
2. Description of the Prior Art
Ultrafiltration is the procedure during hemodialysis wherein excess water is removed from the blood. It is well-known to achieve satisfactory ultrafiltration by maintaining the dialysate pressure within the dialyzer lower than that of the blood pressure. During this procedure, while excess water in the blood is removable, the rate of ultrafiltration is a critical factor, since rapid removal of water from the blood may traumatically affect the patient. Various solutions to the control of the rate of ultrafiltration have been proposed, such as those described in U.S. Pat. Nos. 3,939,069; 4,209,391; and 4,267,041.
U.S. Pat. No. 4,209,391, in particular, achieves ultrafiltration control by utilization of a volumetric system relying upon a principle of volume conservation. In the patented apparatus, a known and equal quantity of fluid is moved into and out of the dialyzer by two matched positive displacement pumps. As dialysate is moved to the dialyzer, a third pump extracts the programmed amount of dialysate from the fresh dialysate supply. The spent dialysate line demands a fixed quantity of fluid and the difference that is drawn off the fresh dialysate supply is made up by the ultrafiltrate drawn across the dialyzer membrane.
In U.S. Pat. No. 3,939,069, a constant volume closed system of hemodialysis is described. A fraction of the dialysis liquid is pumped from the system at a predetermined rate in order to ensure predetermined ultrafiltration flow during a hemodialysis session. The remainder of the dialysis liquid is kept at a constant temperture and is regenerated.
U.S Pat. No. 4,267,041 discloses an apparatus including a plurality of storage containers for the dialysis liquid. These containers are connected in parallel flow arrangement to each other by groups of valves which are controlled by an automatic timer mechanism so that the containers may be operatively connected to the circulatory system in a timed sequence. A branching pump is provided for withdrawing dialysis liquid from the system to control the ultrafiltration in connection with the hemodialysis treatment.
While the inventions described in the foregoing patents represent improvements in controlling ultrafiltration during hemodialysis, further improvements are still being sought. In particular, the desiderata to which such further improvements are directed include simplicity, accuracy and flexibility of use on a variety of dialysis equipment. It is toward the achievement of these desired features and other improved characteristics that the present invention is directed.